1. Field of the Invention
The present invention relates to non-contact type IC cards that transfer data to and from a host system apparatus such as an information processing equipment through non-contact media such as radio waves and the like.
2. Description of the Related Art
Among IC cards that transfer data to and from host system apparatus through non-contact media such as radio waves, a non-contact type IC card illustrated in the block diagram of FIG. 8 is known. Referring to FIG. 8, a non-contact type IC card 100, hereinafter referred to as IC card simply, has a transmitting-and-receiving antenna 102, hereinafter referred to as antenna simply, that transmits radio waves to a host system apparatus 101 and receives radio waves from host system apparatus 101, a modulating circuit 103 that modulates data to be transmitted through antenna 102, a demodulating circuit 104 that demodulates the data received through antenna 102, a UART 105 that converts serial data into parallel data and converts parallel data into serial data, and a memory section 106 that is formed of EEPROM.
IC card 100 further has a control circuit 107 that controls memory section 106, a rectifier circuit 108 that rectifies a radio wave received through antenna 102 to output the rectified power, a regulator circuit 109 that makes constant the voltage of the power output from rectifier circuit 108, to supply the regulated power to each section. The connection between regulator circuit 109 and each section is omitted from FIG. 8.
Host system apparatus 101 comprises a host computer 111 and a data reader-writer 112, hereafter referred to as reader-writer. Reader-writer 112 has a transmitting-receiving antenna 113, hereinafter referred to as antenna, that transmits radio waves to IC card 100 and receives radio waves from IC card 100, a modulating-demodulating circuit 114 that modulates and demodulates data, and a control section that controls modulating-demodulating circuit 114 based on instructions of host computer 111.
In the above construction, the control section 115 of reader-writer 112 controls modulating-demodulating circuit 114 based on instructions of host computer 111 and transfers data through antenna 113. In the case where IC card 100 receives data transmitted from reader-writer 112, the data transmitted from reader-writer 112 is received by antenna 102 and then A/D converted and demodulated into a digital signal by demodulating circuit 104. The demodulated data is serial data. UART 105 converts the serial data into parallel data to output into control circuit 107. Control circuit 107 executes various procedures based on the commands input in this way.
In the case where IC card 100 transmits data stored in memory section 106 to reader-writer 112, control circuit 107 reads the data out from memory section 106 to output into UART 105. UART 105 converts the input parallel data into serial data. The converted serial data is modulated by modulating circuit 103 to be transmitted through antenna 102.
However, the intensity of the electric field strength of a radio waves received by IC card 100 changes depending on the distance between IC card 100 and reader-writer 112, so that the source voltage from rectifier circuit 108 changes. Therefore, the source voltage from rectifier circuit 108 declines, and regulator circuit 109 cannot keep its output voltage constant. As a result, the source voltage supplied to each section declines, and the operation of each section becomes unstable.
Further, in the case where data is written into memory section 106 or the data stored in memory section 106 is deleted, a source voltage greater than a predetermined value is necessary. However, if the source voltage supplied from regulator circuit 109 declines, the writing of data into memory section 106 is not correctly performed, so that the data stored in memory section 106 may be destroyed.
Incidentally, Japanese Pat. Kokai SHO62-154082 disclosed an IC card that is electrically connected to a reader-writer with contact terminals and that has a voltage annunciator that prohibits the writing of data into memory if the source voltage becomes less than a predetermined value. Also, Japanese Utility-Model Kokai SHO61-178548 discloses document-preparation apparatus such as a personal word processor for the Japanese language such that the battery voltage is tested before the writing of data into a floppy disk and the writing is prohibited if the voltage is less than a predetermined value.